Chronic pain due to diabetic neuropathy and other causes can interfere with sleep, which carries a host of secondary complications. Transcutaneous electrical nerve stimulation (TENS) devices provide pain relief by stimulating sensory nerves, which leads to an increase in endogenous opioids and down-regulation of pain signal transmission to the brain. A TENS device which could be used during sleep would offer unique opportunities to provide pain relief during bedtime with the goal of improving sleep (see, for example, Barbarisi M, Pace M C, Passavanti M B, et al. Pregabalin and transcutaneous electrical nerve stimulation for postherpetic neuralgia treatment. Clin J Pain. September 2010; 26(7):567-572).
However, most TENS devices are designed to operate exclusively during the day (i.e., wake state) without any nighttime (i.e., sleep state) operation. This limitation is evident in the design of conventional TENS devices, in which the electric current is delivered through wires (called leads) that are connected to electrode pads on the skin. Such a design is not practical or safe for use during sleep because the leads are cumbersome and may get tangled or pulled, and because the electrode pads can potentially peel off the skin (which will terminate TENS therapy) or, perhaps worse, can potentially partially peel off the skin, leading to increased current density and negative consequences for the user (e.g., discomfort or, in extreme cases, burns).
In pending prior U.S. patent application Ser. No. 14/230,648, filed Mar. 31, 2014 by NeuroMetrix, Inc. and Shai Gozani et al. for DETECTING CUTANEOUS ELECTRODE PEELING USING ELECTRODE-SKIN IMPEDANCE, published as U.S. Patent Application Publication No. US 2014/0296934 A1 on Oct. 2, 2014, which patent application is hereby incorporated herein by reference, there is disclosed a novel TENS device which allows TENS therapy to be applied during nighttime (i.e., during sleep state) as well as during the day (i.e., wake state). The key design elements that make this novel TENS device suitable for use during sleep are (1) the leads are eliminated because the electrode pads are attached directly to the housing containing the TENS stimulation circuitry, (2) the TENS housing and electrode pads are held reliably and comfortably against the skin by an adjustable strap or band, (3) the TENS device continuously measures skin-electrode contact impedance (and related electrical parameters) so as to detect if the electrode pads peel (completely or partially) off the skin and the TENS device stops delivering current if peeling is detected, (4) therapeutic stimulation may be scheduled in one-hour on-off blocks so as to provide pain relief throughout the night, and (5) the TENS device detects when the user is asleep and reduces the therapeutic stimulation level automatically so as not to disturb sleep.
The novel TENS device disclosed in pending prior U.S. patent application Ser. No. 14/230,648 (and published as U.S. Patent Application Publication No. US 2014/0296934 A1) is designed to be located on the upper calf of the user. This is for three reasons. First, the TENS device needs to stimulate sensory nerve fibers in order to provide widespread pain relief through the systemic effect of an increase in endogenous opioids and down-regulation of pain signal transmission. The upper calf area has a cluster of sensory nerve fibers that can be activated easily with a transcutaneous electrical nerve stimulator because of their proximity to the surface of the skin. Second, some forms of chronic pain (such as that due to diabetic neuropathy) are experienced most acutely in the feet, and in addition to the mechanism of pain suppression through endogenous opioids described above (which is systemic), there is also evidence for additional mechanisms of pain suppression that are more local, thus making it advantageous to place the TENS device on the upper calf of the user. Third, chronic pain can be persistent throughout the day, often worsening at night, and wearing the TENS device on the upper calf makes it discreet and unobtrusive, which encourages more regular use.
As mentioned above, the novel TENS device disclosed in pending prior U.S. patent application Ser. No. 14/230,648 (and published as U.S. Patent Application Publication No. US 2014/0296934 A1), which is designed for use during sleep, detects when the user is asleep and adjusts the therapeutic stimulation level to avoid disturbing sleep. It would be advantageous for a TENS device aimed at improving sleep quality to also quantify sleep quality and sleep disorders, since users will be more likely to use the TENS device if they are aware of, and convinced of, its benefit to their sleep.
The gold standard in determining the sleep-wake state of a subject is polysomnography which comprises at least three distinct types of data, i.e., electroencephalogram (EEG), electrooculography (EOG) and electromyography (EMG). Because of the difficulty in recording and analyzing these types of data, actigraphy has been developed and refined over the last 30 years as a practical alternative to study sleep/awake patterns. Actigraphy is a continuous recording of body movement by means of a body-worn device, typically equipped with accelerometers [Ancoli-Israel S, Cole R, Alessi C, Chambers M, Moorcroft W, Pollak C P. The role of actigraphy in the study of sleep and circadian rhythms. Sleep. May 1 2003; 26(3):342-392].
Wearable electronic devices for health and fitness have become widespread, and most have accelerometers and, from acceleration data, compute various metrics of activity either to track daytime activities or to quantify sleep patterns. Most of these actigraphy-based devices are worn on the wrist however, and in certain ways that limits their ability to detect and quantify sleep.